5. Eat Lean Protein With Every Meal

Protein is the building block of muscle — and if you’re struggling to gain size, chances are you don’t get enough. Eat at least two servings of lean protein with every meal, which is roughly the size of two decks of cards.

If you shortchange your protein, you’ll have to get more of your calories from carbs and fat. Unless you’re Michael Phelps, that combination will only lead to more body fat, not muscle.